Power switches with only two states of ON/OFF function controlled manually have been widely used in many appliances. However, it is risky to use the above power switches when the power source is unstable because overheating may occur due to overloading of the appliance and the wire easily catches fire. The user can not be aware of such latent danger since overloading and overheating are invisible. Therefore, improved power switches have been greatly needed to overcome the danger.
Some improved power switches in the prior arts includes an alloy element composed of more than one metal to automatically shut off the power source when the alloy element is thermally deformed because of overheating.
For example, a conventional power switch comprises an alloy piece, a lever, and a cam actuator. The lever is actuated by the alloy piece, and the cam actuator is used to coordinate with a seesaw actuator. Thermal deformation of the alloy piece causes the lever to move, and then the cam actuator loses support, escapes and further shuts off the power source. Overheating may occur on he alloy piece. The above power switch uses the lever, the cam actuator, and the seesaw actuator to indirectly control the conductive plate, which is used to contact with the power source. The response of the power off operation in the above power switch when overheating occurs is so slow that the overloaded current may flow into the operating appliance in a short time to damage the appliance. Additionally, the conductive plate and the alloy piece need the wire to connect to each other, and the whole structure is complicated to cause the manufacturing difficult. The alloy piece has to actuate the seesaw actuator and the lever to escape. The function of automatic power off may incorrectly operate.
Furthermore, another conventional power switch uses the thermal deformation of the alloy piece to push a limited position base such that a button can automatically escape and return back. The button is used to directly contact with the contact point of the power source so that the button may conduct the overloaded current when overheating occurs. The whole structure is still complicated. In summary, those improved power switches in the prior arts can partly overcome the danger of overheating for the appliance but the response is slow and the whole structure is complicated. An advanced power switch with simpler structure and a short response time is greatly desired.